Interpretive Summary: The development of alternative methods for controlling postharvest fruit decay are being prompted by the consumer's demand for pesticide-free produce. Previous work has shown that the postharvest treatment of apples with calcium is beneficial in maintaining fruit quality by decreasing decay due to fungal pathogens. One possible effect of calcium in reducing decay is through the direct effect of calcium on the fungus itself. The results of this research project indicate that increasing the amount of calcium in fungal growth media leads to increased take-up of calcium and development of thicker cell walls, which are sugar envelopes surrounding each fungal cell. The thickening of the cell walls may then retard elongation of the mycelium and result in a loss of cell wall elasticity. This would slow the growth rate of the fungus and retard decay. Increasing the calcium concentration in apple fruit could help the grower maintain fruit quality and reduce his dependency on fungicides.

Technical Abstract:
Increasing the calcium (Ca) content of fruits and vegetables has been shown to reduce decay caused by Botrytis cinerea, an important postharvest pathogen. The goal of this study was to determine whether Ca has an effect on the chemistry of the fungal cell wall. Botrytis cinerea was grown on Richard's solution containing different amounts of CaCl2 and the cell walls extracted from the mycelium after 7 days of growth. Mineral, neutral and aminosugar, protein and uronic acid contents were determined. At 1 g/l CaCl2 only the aminosugar content increased. At 2 g/l CaCl2, neutral sugar synthesis was reduced, whereas uronic acid content increased. For higher CaCl2 concentrations, the calcium content of the cell wall increased, resulting in reduced protein and neutral sugar contents. Meanwhile, the cell wall proportion of the mycelia increased on a dry weight basis, due to an increase in uronic acid, Ca, P, Na and neutral sugar contents of the cell wall with increasing CaCl2 in the media.